docs: def header(self):
          '''
          Provide PLY-formatted metadata for the instance.
  
          '''
          lines = ['ply']
  
          if self.text:
              lines.append('format ascii 1.0')
          else:
              lines.append('format ' +
                           _byte_order_reverse[self.byte_order] +
                           ' 1.0')
  
          # Some information is lost here, since all comments are placed
          # between the 'format' line and the first element.
          for c in self.comments:
              lines.append('comment ' + c)
  
          for c in self.obj_info:
              lines.append('obj_info ' + c)
  
          lines.extend(elt.header for elt in self.elements)
          lines.append('end_header')
          return '\n'.join(lines)